Chronocoulometry of wine on multi-walled carbon nanotube modified electrode: Antioxidant capacity assay.

Phenolic antioxidants of wine were electrochemically oxidized on multi-walled carbon nanotubes modified glassy carbon electrode (MWNT/GCE) in phosphate buffer solution. Three oxidation peaks were observed at 0.39, 0.

Chronoamperometric estimation of cognac and brandy antioxidant capacity using MWNT modified glassy carbon electrode.

Cognac and brandy components are electrochemically oxidized on multi-walled carbon nanotube modified glassy carbon electrode at 0.44 and 0.59 V in 0.

Coulometric titration with electrogenerated oxidants as a tool for evaluation of cognac and brandy antioxidant properties.

Stoichiometric coefficients for reactions of cognac antioxidants with coulometric titrants (electrogenerated bromine and hexacyanoferrate(III) ions) have been found. Ellagic and gallic acids react with both titrants while aldehydes (vanillin, syringic and coniferaldehyde) - with electrogenerated bromine only. Furfurals do not show significant reactivity toward both oxidants.

Electrochemical DNA sensors based on electropolymerized materials.

The use of electropolymerized materials in the DNA sensors is reviewed with particular emphasis on their functions and specific interactions with DNA and oligonucleotides. Polyaniline, pollypyrrole, polythiophenes and polymeric forms of phenazines play significant role in the immobilization and signal transduction of DNA sensors for the detection of hybridization events, DNA-protein and other specific interactions on the sensor surface. The mechanism of electropolymerization and the influence of oligonucleotides are also considered for various types of polymers.

Voltammetric determination of β-carotene in raw vegetables and berries in Triton X100 media.

Electrochemical behavior of β-carotene in polar organic media and solubilized systems has been investigated. β-Carotene is irreversibly oxidized at 500 and 920 mV on glassy carbon electrode in 0.1 M LiClO(4) ethanol containing 10% of CH(2)Cl(2).

Surfactant media for constant-current coulometry. Application for the determination of antioxidants in pharmaceuticals.

Effect of surfactant presence on electrochemical generation of titrants has been evaluated and discussed for the first time. Cationic (1-dodecylpyridinium and cetylpyridinium bromide), anionic (sodium dodecyl sulfate) and nonionic (Triton X100 and Brij(®) 35) surfactants as well as nonionic high molecular weight polymer (PEG 4000) do not react with the electrogenerated bromine, iodine and hexacyanoferrate(III) ions. The electrogenerated chlorine chemically interact with Triton X100 and Brij(®) 35.

Discrimination of apple juice and herbal liqueur brands with solid-state electrodes covered with polyaniline and thiacalixarenes.

Solid-contact ion-selective electrodes based on glassy carbon electrode covered with electropolymerized polyaniline and tetrasubstituted thiacalix[4]arene ionophores with hexyl and o-pyridylamido functional groups at the lower rim have been developed and examined in the discrimination of the brands of apple juices and herbal liqueurs. For this purpose, the liquids tested were diluted and spiked with a constant amount of Fe(3+) ions. The variation of the signal toward Fe(3+) ions was achieved due to their involvement in the reactions with the organic ligands and the antioxidants present.

The application of coulometry for total antioxidant capacity determination of human blood.

New coulometric method for estimation of blood and plasma total antioxidant capacity (TAC) based on using electrogenerated bromine was proposed. TAC of blood from patients with chronic renal disease undergoing long-term hemodialysis was investigated. Statistical significant changes in TAC level of venous and arterial blood were found.

Amperometric biosensors based on nafion coated screen-printed electrodes for the determination of cholinesterase inhibitors.

Screen-printed electrodes coated with the nafion layer have been investigated for cholinesterase biosensor design. The butyrylcholinesterase (ChE) from horse serum was immobilised onto the nafion layer by cross-linking with glutaraldehyde vapours. The biosensors obtained showed better long-term stability and lower working potential in comparison to those obtained with no nafion coating.

Sensitivity and selectivity of electrochemical enzyme sensors for inhibitor determination.

The performance of electrochemical biosensors developed for the determination of inhibiting species is considered. The role of various factors affecting the analytical characteristics of biosensors, their selectivity toward inhibitors to be tested as well as operational characteristics is discussed. The choice of enzyme-inhibitor system, the influence of enzyme immobilization on the behaviour of a biosensor, the modes of the optimization of working conditions are discussed.

Selectivity of solid-contact Ag potentiometric sensors based on thiacalix[4]arene derivatives.

Potentiometric sensors based on glassy carbon electrode covered with polyaniline and thiacalix[4]arenes containing amidopyridine, morpholide, pyrrolidide and hydrazide functional groups in cone, partial cone and 1,3-alternate conformations have been developed and applied for determination of Ag(+) ions in the range from 1.0 x 10(-2) to 4.0 x 10(-7)M and limits of detection from 1 x 10(-7) to 3.

Ag selective electrode based on glassy carbon electrode covered with polyaniline and thiacalix[4]arene as neutral carrier.

Potentiometric sensor based on glassy carbon electrode covered with polyaniline and neutral carrier, e.g. thiacalix[4]arene containing pyridine fragments in the substituents in the lower rim has been developed and applied for determination of Ag(+) ions in the range from 1.

Amperometric immunosensor for nonylphenol determination based on peroxidase indicating reaction.

Novel immunosensor for nonylphenol (NP) determination has been developed by immobilization of specific antibodies together with horseradish peroxidase on the surface of carbon screen-printed electrode. The signal of the immunosensor is generated by the involvement of NP accumulated in the peroxidase oxidation of mediator (Methylene Blue, hydroquinone or iodide). This results in the increase of the signal recorded by linear-sweep voltammetry.

Application of constant-current coulometry for estimation of plasma total antioxidant capacity and its relationship with transition metal contents.

Simple and express coulometric method for the evaluation of the total antioxidant capacity (TAC) of human plasma based on the reaction with electrogenerated bromine is applied. TAC of plasma from patients with different ethiology of chronic renal failure was observed. The levels of antioxidant capacity for venous and arterial plasma are authentically different (15+/-1 kCl/L versus 11.

Acetylcholinesterase sensor based on screen-printed carbon electrode modified with prussian blue.

Acetylcholinesterase (ChE) sensor based on Prussian blue (PB) modified electrode was developed and tested for the detection of organophosphorus and carbamic pesticides. The signal of the sensor was generated in PB mediated oxidation of thiocholine recorded at +200 mv in DC mode. ChE from electric eel was immobilized by cross-linking with glutaraldehyde in the presence of bovine serum albumin (BSA) on the surface of screen-printed carbon electrode covered with PB and Nafion.

Electrochemical determination of the total antioxidant capacity of human plasma.

Electrochemical reduction of oxygen at a glassy carbon electrode in a 0.05 mol L(-1) solution of (C2H5)4NI in dimethylformamide leads to generation of the superoxide anion-radical. This product of reversible one-electron oxygen reduction reacts with antioxidants, a process which is based on protonation of the anion-radical by the antioxidant.

Bi-enzyme sensor based on thick-film carbon electrode modified with electropolymerized tyramine.

Bi-enzyme sensor based on thick-film epoxy-carbon electrode modified with polytyramine has been developed and examined for the determination of peroxidase substrates and cholinesterase inhibitors. Polytyramine was obtained on the electrode surface by repeated scanning of the potential from +600 to +1800 mV vs. Ag/AgCl in tyramine solution.

Cholinesterase sensors based on screen-printed electrodes for detection of organophosphorus and carbamic pesticides.

Cholinesterase sensors based on screen-printed electrodes modified with polyaniline, 7,7',8,8'-tetracyanoquinodimethane (TCNQ), and Prussian blue have been developed and tested for detection of anticholinesterase pesticides in aqueous solution and in spiked grape juice. The influence of enzyme source and detection mode on biosensor performance was explored. It was shown that modification of the electrodes results in significant improvement of their analytical characteristics for pesticide determination.

Polyaniline-modified cholinesterase sensor for pesticide determination.

Cholinesterase sensors based on glassy carbon and planar epoxy graphite electrodes modified with processed polyaniline have been developed and examined for pesticide detection. The modification of electrode surface with polyaniline provides high operational stability and sensitivity towards the pesticides investigated. The detection limits found (coumaphos, 0.

Influence of surface-active compounds on the response and sensitivity of cholinesterase biosensors for inhibitor determination.

The influence of non-ionogenic surfactants, i.e., Tween-20, Triton X-100 and PEG-10,000, on the response of cholinesterase-based potentiometric biosensors and their sensitivity towards reversible and irreversible inhibitors were investigated.

New variants of enzyme immunoassay of antibodies to DNA.

A method of DNA immobilization on cellulose nitrate films has been developed. Modified films of uniform and stable surface have been used to devise two variants of solid-phase enzyme immunoassays of antibodies. The co-immobilization of enzyme label (cholinesterase) and the DNA molecules makes it possible to carry out the procedure of solid-phase enzyme immunoassay without any separation of components.

Determination of hydrazine derivatives by flow-injection analysis with spectrophotometric detection.

Flow-injection analysis for the determination of hydrazine derivatives based on their nucleophilic substitution reaction with 4-chloro-5,7-dinitrobenzofurazan in aqueous medium, and spectrophotometric detection has been described. The calibration graphs were linear in the range from 0.15 to 4.

Electrochemical investigation of palladium complexes with organic sulphides and their use in extraction differential pulse polarography.

Dialkyl-, amino-, keto- and ketoaminosulphide complexes of palladium(II) are shown to undergo one- or two-step reduction in a mixed acetonitrile-toluene solvent containing Bu(4)NClO(4) at 0.1 M concentration. The half-wave potentials of the complexes show a certain dependence on the ligand structure, a positive shift of the potentials being caused by an increase in the pi-acceptor ability of the ligands.

The stability of metal complexes with 8-mercaptoquinoline and alkyl-substituted 8-mercaptoquinolines in dimethylformamide.

The stoichiometry and stability constants of 8-mercaptoquinoline and alkyl-8-mercaptoquinoline complexes of Zn(II), Cd(II), Pb(II), Ni(II), Bi(III) and Ag(I) were determined potentiometrically in dimethylformamide. The stability of the 8-mercaptoquinolinates decreases in the order Ag(I) Bi(III) Ni(II) Pb(II) Cd(II) Zn(II). Metal 7-methyl-8-mercaptoquinolinates are the most stable.